Genesis of a Champion - Porsche 917

What made the 917 such an unbeatable competitor? We look deep under the skin

Feature Article from Hemmings Sports & Exotic Car

The Porsche 917 exists in the land of the superlative, universally revered and often the beginning and end of discussions regarding "the best race car ever."

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Porsche was no stranger to success before 1970, having won class victories more than a few times at Le Mans, as well as countless other endurance titles around the world. But they had never tasted the champagne as the overall victor at the famed 24-hour race until they had the 917 in their arsenal.
Created by a team led by chief engineer Ferdinand Piëch, the 917 laid the groundwork for a series of endurance sports racers that would dominate the sport for decades. Basing the design of the 917 on the successful 908, Piëch's squad took advantage of a loophole in the rules that allowed for the use of a five-liter engine if 25 examples could be produced in a year. When Porsche decided in mid-1968 to make such an attempt, it had 10 months to get the job done in order to get the FIA to homologate it for 1969.
Porsche completed the task on time, though the 917 was not competitive out of the box. Undeniably very powerful and blindingly fast, the 917 proved virtually undriveable at speed. Jo Siffert called it "unstable" and "dangerous." The death of privateer John Woolfe in a fiery crash in a 917 on the first lap of Le Mans in 1969 did little to endear the car to drivers and led directly to the demise of the traditional "Le Mans"-style start. The other two 917s in the race later withdrew due to mechanical failure, though Vic Elford was leading by 50 miles at the 21-hour mark when the bell housing of the transaxle cracked.
Vic, who has frequently gone on record stating that the 917 was his favorite car, "including that almost undriveable monster" from 1969, spoke with HS&EC about his experiences with the 917. "The first year, 1969," says Vic, "it was pretty unstable to such a point that, for example, on the Mulsanne straight at Le Mans, coming to the kink, you couldn't just lift off, you had to ease back on the throttle. You had to ease back on the throttle and then go easy and very gently onto the brakes. Aerodynamics were in their infancy then and nobody knew much about them, including even Piëch. What happened at high speed was that if you snapped off the throttle, the back end just sort of came up in the air and started steering the front, which at 220 MPH wasn't really very nice."
In 1969, the veteran 908 proved more competitive, despite all the seeming advantages of the 917. At the end of the season, Porsche hired John Wyer so that they could concentrate on the engineering and production end. In a case of aerodynamics by entomology, Wyer's chief engineer, John Horsman, observed that there were hardly any gnats splattered on the rear wing during a very buggy test session--the tail section simply wasn't getting enough airflow to create any significant downforce. The Wyer crew cobbled together a shorter raised tail section to test Horsman's theory. Brian Redman almost immediately started lapping several seconds faster and returned to the pits, declaring, "That's it--now it's a racing car!" The factory soon got to work revising the 917's body and the short-tail 917K was born. Victories began piling up for the 917 in 1970, including at Le Mans, where it even bested the revised long-tail 917LH with sustained speeds in excess of 220 MPH. Porsche repeated the Le Mans victory in 1971, setting a total distance record not surpassed until 2010.
Recently, we had the chance to get up close and personal with a 917K during a Sportscar Vintage Racing Association event at Watkins Glen. Owned by Greg Galdi, of Long Island, New York, this particular 917K never turned a wheel in competition. Its chassis, bearing serial number 037, was held as a spare when new. Never needed as a replacement for a damaged car, it was purchased--along with a host of spares--by Vasek Polak, the West Coast Porsche dealer. Polak's longtime parts manager, Carl Thompson, acquired the chassis and almost every component needed to create what is essentially a new-old-stock 917, including a 4.9-liter version of the vaunted flat-12 engine.
Thompson assembled the car about 15 years ago and had a new fiberglass body created by noted Florida-based Porsche racing and restoration shop Gunnar Racing, led by Kevin Jeannette. Gunnar molded the body from an original 917K, and handled the rest of the coachwork required to complete the car. This particular Martin & Rossi livery, as raced by Vic Elford and Gijs Ven Lennep at Daytona in 1971, was chosen not only for the way the nearly flawless silver paint flatteringly shows the 917K's graceful lines, but also because the original suffered significant damage at Daytona and was refinished in a different paint scheme. This choice allows Galdi to race and display 917-037 in the glorious, authentic Martini colors without bringing into question the provenance of any other 917s.
ENGINE
The rapid gestation of the 917 program meant that the engine itself skipped the usual prototyping stages, not even running the first time until just weeks before the car's March 1969 introduction. Following on the same basic architecture that Porsche cars had used since day one, the 12-cylinder engine featured air and oil cooling and two horizontally opposed cylinder banks. It was their largest displacement engine to date.
Initially 4.5 liters, the engine featured a magnesium crankcase vertically split from front to back, held together by special alloy bolts. The forged crankshaft had eight main bearings and six crankpins that each shared a pair of titanium connecting rods for the engine's twelve pistons reciprocating in individually bolted-on, cast-aluminum cylinders with chrome-plated bores.
With a 120-degree firing order, the engine had more inherent balance than the eight-cylinder 908, though it had the same 85 mm by 66 mm bore and stroke of the 908. When engineers calculated that the ends of the long crankshaft would experience second-order oscillations resulting in significant vibrations, they designed the engine's power takeoff to come from the center of the crank.
On the bottom of the engine, the center gear drove a propshaft that transferred torque back to the clutch at the transaxle and also powered the multiple oil pumps. From above, the gear powered the four camshafts, two per side that operated a single intake and exhaust valve on each cylinder. The center takeoff gear also powered the top-mounted fiberglass cooling fan via a bevel gear. The fan required as much as 17 hp to run at 90 percent engine speed and could move up to 5,100 cubic feet of air per minute.
Although the fan provided approximately 80 percent of the cooling necessary for the 917, like all air-cooled engines, its powerplant relied on proper oil cooling to maintain temperature. A thermostatic valve in the dry-sump oiling system (capacity was a voluminous 21 quarts) would open when the lubricant hit 185 degrees to send oil to a large, multi-row oil cooler mounted in the nose of the car.
Despite the rapid development time and minimal bench testing, the initial 4.5-liter flat-12 produced 580 hp and 376-lb.ft. of torque, a massive leap from the 360 hp or so that the 3.0-liter flat-eight in the 908 made. A further evolution for 1970, with bore and stroke increased to 86 mm and 70.4 mm, respectively, resulted in 600 hp from 4.9 liters that moved the 1,760-pound sports car with an intensity unlike any other Porsche before it and very, very few after it.
TRANSMISSION
Though substantially beefed up over its predecessor's transaxle, the 917's five-speed gearbox shared much with the 908's design, though it was carried in a magnesium alloy case instead of aluminum. Given the overall low position of the engine, the clutch disc itself had to be quite small to fit, and at just 7.28 inches in diameter, it did initially prove a vulnerable point in the 917's otherwise robust driveline.
The shift linkage was on the right-hand side of the right-hand-drive car, a traditional placement in sports racers. Less traditional was the dogleg gearbox with fifth gear down and to the right of the H-pattern. Drivers had to learn to be extra careful when shifting from fourth to fifth so as to avoid a fourth-to-third swap that had the potential to terminally over-rev it.
CHASSIS
Though the initial run of 908s had been fabricated from triangulated steel tubes, the later, extremely lightweight 908/3s were all made from triangulated aluminum tubing. Again, with the compressed time frame given the 917, the engineers used the same wheelbase of the successful 908 and almost identical front and rear track widths. Porsche used five different types of aluminum tubing, in various diameters and wall thicknesses, depending on the strength required in that particular section. The entire frame weighed in at a svelte 104 pounds. Given the minimum weight of 1,760 pounds for Group 4 cars, Porsche could build the chassis for strength over lightness.
SUSPENSION
The 917 carried a rather conventional suspension with unequal length A-arms front and rear with coil springs mounted over Bilstein hydraulic shock absorbers. Porsche engineers designed the front suspension geometry to counteract brake dive while the rear, aided by two radius rods per side, was designed to keep the wheels out of positive camber.
Where the 917 veered from convention was that the springs were made from titanium wire. The rack-and-pinion steering carried a rather fast 11.4:1 ratio with just 1.75 turns lock to lock. Initially made from steel, the rack, too, was later machined from titanium.
BRAKES
Just as it had the most powerful engine in a Porsche up to that point, so, too, did the 917 have the largest brakes. With 12-inch rotors in front and 11.4-inchers in the rear, the 917 made the most of them with twin master cylinders and driver-adjustable brake bias.
Along with mounting four-piston aluminum calipers, Porsche saved unsprung weight by mating the cast-iron discs with aluminum carriers via axially mounted screws so that, even as the metals expanded at different rates, the complete rotor would stay together under the most extreme conditions. Continuing the theme of exotic or lightweight metals throughout the car, engineers specified titanium hubs as well.
BODY/AERODYNAMICS
The original idea behind the 917 was to supply each car with a pair of swappable rear sections for the all-fiberglass body: a long tail for high-speed courses and a shorter one for tighter, more technical circuits. Unfortunately, neither tail turned out to offer high-speed stability. Pretty much any race car could kill you in 1969, so not many drivers were too keen to have a car steer itself at 200 MPH or more.
After initially speculating that the instability stemmed from chassis problems, it took Wyer's team and the bug-splatter incident during testing to sort out the aerodynamics, which immediately cured the stability issues. With this newfound knowledge in hand, the factory went back to the drawing board and fashioned a newer, upswept rear end with a truncated back, giving birth to the 917K--for kurzheck, or short tail--for the 1970 season, and ultimately, the revised long-tail 917LH that won at Le Mans.
Vic, even as much as he embraced the first "monster" 917, recognizes advances made for 1970. "By the time we got to Argentina for the first race of 1970," he says, "the short-tail, as it then became known really, was superbly stable. It was comparatively easy to drive. It was a beautiful car to drive, absolutely beautiful, right from the word 'go.'"
If not for Horsman's keen observation, the Porsche 917 might have remained just a sideshow of occasionally freakish speed. Instead, it became so dominant in just two years that the FIA essentially outlawed it by drastically increasing the homologation minimum for Group 4 production cars. But with the 917 experience fresh in hand, Porsche still spent the next 30 years being the team to beat at Le Mans. They'll get a chance to add to that record this June, with their return to La Sarthe for the first time since 1998.
Specifications

Engine
Type: Type 912 DOHC flat-12
Displacement: 4,907 cc (299.5-cu.in.)
Bore x stroke: 86 x 70.4 mm
Compression ratio: 10.5:1
Horsepower @ RPM: 600 @ 8,300
Torque @ RPM: 405-lb.ft. @ 6,500
Fuel delivery: Bosch Kugelfischer mechanical fuel injection
Transaxle
Type: Five-speed manual transaxle
Ratios: Varied depending on track
Steering
Type: Rack and pinion
Brakes
Type: Four-wheel vented discs with four-piston aluminum calipers
Front: 12 inches
Rear: 11.4 inches
Weights and Measures
Wheelbase: 90.6 inches
Overall length: 162.2 inches
Overall width: 78 inches
Overall height: 36.2 inches
Weight: 1,760 pounds
Performance
Top speed: 220 MPH
Price
New: 140,000 Deutsche Marks(approximately $35,000)
Porsche 917
Owner's Story
I try to take the 917 out whenever I can, just so that people can see it at least. At Watkins Glen, I take it into town and do the old circuit on it. When that thing comes down the road, it makes a great screaming sound. The view out of the front of that car is terrific. You see right in front of you. The nose really drops off, so you see really well.
There's no feeling like coming down that straightaway and pressing that pedal down. It's got a very long travel and you push that down and you just feel that torque propel you. It's a car that demands respect because of its horsepower. You have The 917's driver had a tachometer and gauges for oil temperature and oil pressure--all of the critical information he needed and nothing else to distract him at speed. Warning lights were used for other problems and the fuse panel was immediately at hand. Even the key is cross-drilled for lightness. some big, fat tires on it, but they're grooved, so you've got to give the torque some respect. But it's a great chassis and it's very communicative to the driver and it tells you what it's doing. It really scoots along with all of that torque. -Greg Galdi
Getting 600 horsepower to the ground required lots of grip from the tires--12 inches wide at the front and 18 inches at the rear. Five-spoke wheels were cast of a magnesium alloy that contained nine percent aluminum and one percent zinc and were held down on titanium hubs by forged aluminum central locking nuts.The 917 was designed with much lower rear flanks, but a race-team engineer discovered during a test that, while the front of the car was killing bugs well and good, the rear spoiler was practically free of splatter. A revised, upswept rear section with a truncated tail vastly improved the car's stability at speed.Wind-tunnel experiments with a scale model suggested keeping vents and ducts to a bare minimum, but a year of racing and real-world testing resulted in wider and deeper ducts and vents to improve airflow and stability.Don't be fooled that the 917 featured an air-cooled engine. Oil handled at least 20 percent of the required cooling on the highly stressed racing powerplant. A thermostatic valve in the oil system would open to direct engine oil to the nose-mounted cooler when lubricant reached 185 degrees Fahrenheit.Feeding the 12, deep-breathing, hungry cylinders was a Bosch Kugelfischer mechanical fuel-injection pump, driven by a belt run off the end of one of the four camshafts.Keeping temperatures under control on the big 12-cylinder engine was a six-blade, 13-inch fan. Driven by the top of the engine's center power-takeoff gear via a bevel drive, the fan was able to move up to 5,100 cubic feet per minute. Its airflow requirements had to be accommodated during indoor dyno runs.Porsche engineers fitted the 917 engine with dual distributors, each connected to 12 spark plugs for the twin-plug, two-valve engine. A distributor at the front of the engine fed the front six cylinders and a distributor at the back handled the rear six cylinders.

This article originally appeared in the June, 2014 issue of Hemmings Sports & Exotic Car.